For scalable video codecs (SVC), e.g., H.264 SVC or H.265 SVC, layers in addition to the basic layer ensure higher video quality levels and enable an adaption of the video quality of an already encoded video stream.
Nowadays, RTP control protocol (RTCP), as a band-internal feedback channel within Real-time Transport Protocol (RTP) from the target node(s) to the source node(s), carries information from which the actual end-to-end network service quality at the source node (e.g., packet loss rate, delay, jitter) can be derived. Based on this information, the encoder is able to start or restart the generation of additional layers at the source node for transmission, reduce the image frequency or frame rate or increase the compression ratio to reduce bandwidth consumption. To facilitate this, the end-to-end link is identified through a relationship between source node connection and target node connection. This concept also applies to point to multipoint connections, e.g., for video distribution services.
Another known concept dedicated to H.264 SVC is an intelligent router on which (mobile) devices or terminals register their capabilities, e.g., screen size, resolution, etc. The available bandwidth toward the device is also taken into account. The video source generates all layers of the SVC codec. This video stream is passed on via an intelligent router that decides for each individual target device how many layers will be passed on to that device based on the registration information. Accordingly, individual video streams are forwarded for each connection endpoint.
PPP-Multilink [RFC1990] describes, for example, bundling multiple links into one virtual link in the link layer. This conceals information about the differences between the access technologies used, and no further adaption of the transport layer with respect to different linking qualities is possible.
Multipath-TCP [RFC6824] allows different network paths to be exhausted by using subflows or partial flows. However, only one single transport service is provided for applications (i.e., reliable transport).